1. Technical Field
The invention relates to a device for establishing a call connection, a subscriber terminal with such a device, a telecommunication system with such a device, and a method for establishing a call connection.
2. Discussion of Related Art
An article by Dirk Reusch, xe2x80x9cTelefonieren xc3xcber das Internetxe2x80x9d, [Telephoning via the Internet] Funkschau 17/95 pp. 44-47, describes how a packet-switched data network, namely the Internet, can be used for telephone calls and thereby for the establishment of a call connection between two subscriber terminals. To that end, speech is digitized, compressed, transmitted in packets by way of the Internet, and on the other end, is reconstituted, decompressed, and digital-analog converted. This type of telephony can save a considerable amount of telephone charges. Internet telephony gateways serve to connect the Internet to the conventional telephone network in order to thus produce a telephone call between an internet subscriber and a subscriber to the conventional telephone network. Telephony via the Internet, however, has the disadvantage of fluctuating transmission quality, since no fixed bit rate for data transmission is guaranteed on the Internet. This can lead to halting speech transmission, call pauses, or also call interruptions due to the exceeding of a time limit.
The article xe2x80x9cJackpot Least-Cost Routingxe2x80x9d by Ulrich Pfaffenberger, which appears in Funkschau 9/97, pp. 28-34, describes a possibility for savings on telephone charges in calls to mobile radio subscribers. To this end, so-called connecting boxes are used, which determine whether a subscriber can be reached by way of a mobile radio network or by way of a fixed network. Both networks are connection-oriented telecommunication networks. The connecting box has a direct connection both to the fixed network and to various mobile radio networks and in conjunction with the phone number of the desired calling partner, selects which network is used to produce a connection. This method, which is called least-cost routing, has the disadvantage that it can only be used in calls to mobile radio subscribers.
The object of the invention is to produce a device for establishing a flexible call connection between subscriber terminals in which a significant impairment of speech quality does not occur. Another object of the invention is to disclose a method for establishing such a call connection.
One advantage of the invention is that with the current pricing policy of network providers, a cost savings is achieved in relation to phone calls in the conventional telephone network.
According to a first aspect of the invention, a device for establishing a call connection between at least two subscriber terminals, which has a first interface to a packet-switched data network and means for establishing connections by way of the packet-switched data network, is characterized by means of
a second interface to a connection-oriented telecommunication network, in which a transmission channel with a set transmission band width can be furnished,
a monitoring device for determining a current data throughput in the data network,
a control device for comparing the current data throughput with a set threshold value and for controlling the establishment of connections in such a way that the call connection is established by way of the data network when the data throughput lies above the threshold value and is established by way of the telecommunication network when the data throughput lies below the threshold value.
According to a second aspect of the invention, a subscriber terminal in which two channels to a digital, connection-oriented communication network can be furnished in parallel, characterized in that it contains a device according to claim 1, that the first interface and the second interface are respectively connected to one of the two channels, and that a connection to a provider of the packet-switched data network can be furnished by way of the channel connected to the first interface.
According to a third aspect of the invention, a telecommunications system with a large number of connections for subscriber terminals, is characterized by means of a device according to claim 1.
According to a fourth aspect of the invention, a method for establishing a call connection from a calling subscriber terminal, which is connected to a device for establishing the call connection, to at least one called subscriber terminal, with the following steps:
connection of the calling subscriber terminal with a packet-switched data network by way of a first interface of the device,
connection of the calling subscriber terminal to a connection-oriented telecommunication network, in which a transmission channel with a predetermined transmission band width can be furnished, by way of a second interface of the device,
determination of a current data throughput in the packet-switched data network,
comparison of the current data throughput with a predetermined threshold value, and
control of the establishment of connections in such a way that the call connection is established by way of the data network when the data throughput lies above the threshold value and is established by way of the communication-oriented telecommunication network when the data throughput lies below the threshold value.